Caple C871i Bedienungsanleitung PDF herunterladen (Seite 221)

100

101

Apple II Computer Info

loop2 iny ; increment pdl1 counter

lda pdl1 ; is high bit = 0?

bmi loop2 ; no, keep checking

plb ; yes, restore data bank

plp ; and processor status register

rts ; return to caller (could be RTL)

Notice that the actual counting loops are only 9 cycles long. This gives the

best possible resolution. You will need your counters to be 16 bits wide as

the results will easily overflow the capacity of an 8 bit counter. Using

memory locations as counters will only serve to slow the counting loop down.

If X and Y contain valid data before entry, you will need to save them off to

the stack and pull them back in after interpreting the joystick results.

I have used this exact method to read the analog inputs on my Science Toolkit

box which connects to the joystick port. The results have been extremely

accurate (much more than would be needed for a game which reads the joystick).

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ProLine: tgeer@pro-gumbo Internet: [email protected]

UUCP: crash!pro-gumbo!tgeer Fidonet: [email protected]

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"My wife is a bargain hunter - I just carry the ammunition."

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### joystck.read

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Apple II Computer Technical Information : Apple II Family Hardware Info

ftp://ground.ecn.uiowa.edu/2/apple2/miscinfo/hardware : May 2001 : 221 of 572

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